The present invention concerns an active suspension system for vehicle level control under either manual and/or automatic control.
Vehicle suspension systems perform various functions that affect the ride of the motor vehicle. A vehicle suspension system includes various different elements such as springs, shock absorbers, mechanical linkages, and structural members to xe2x80x9csuspendxe2x80x9d the mass of the motor vehicle.
Springs provide an upward force against the vehicle frame and the force is related to an amount of deformation of the spring. Spring types include coil springs, leaf springs, bar springs, torsion springs and gas springs.
Shock absorbers provide a force related to the rate of change of an extension of the shock absorber component. A typical shock absorber utilizes hydraulic oil to damp motion via fluid flow impedance through at least one flow-restricting orifice. Improved shock absorbers incorporate at least one pressure-actuated valve providing variable damping via multiple orifice and/or variable orifice size to provide variable net damping based upon position and/or dynamic conditions. Gas-assist shock absorbers further incorporate internal gas springs and valves to significantly reduce damping of rebound relative to jounce to reduce rebound time and maintain more average height.
More advanced shock absorbers use electro rheological and magneto rheological fluids with active control of fluid viscosity through an orifice to vary motion damping. Major drawbacks to utilization of electro rheological (ER) fluids include moisture susceptibility, contamination susceptibility, and very high voltage requirements. Response time for magneto rheological (MR) fluids from Lord Corporation is reportedly less than 25 ms to 50 ms. Advantages of MR fluids relative to ER fluids include lower material cost, much lower susceptibility to moisture contamination, and low drive voltage requirements.
Vehicle performance and handling improvements enabled by dynamic stability controls and electronic suspensions are becoming more practical when powered by higher voltages as for example new proposed 42 volt DC supplies. Peak and average power loads reported for a typical active suspension system are 12 KWatt and 360 Watt, respectively. Technological advancements in sensing, computing, suspension mechanisms, fluid power, electrical power, and controls result in various active system control implementations responding to multiple static and dynamic vehicle and suspension unit inputs.
One prior art active suspension (Davis U.S. Pat. No. 5,060,959) for a vehicle includes an electrically powered device acting either alone or in parallel with a static load carrying device such as a fluid spring or coil spring. Another prior art active suspension system (Yopp U.S. Pat. No. 5,322,321) incorporates multiple dual suspension units, each including an electrically powered actuator for slower force adjustments combined with a gas assist spring for faster force adjustments utilized either alone or with other type active suspension systems such as electromagnetic, hydraulic, or hydro pneumatic for actively adapting vehicle ride height. Dynamic suspension systems employ the function of changing spring rate and damping force in accordance with driving conditions and road surfaces.
To overcome limitations of fixed rate damping and spring element systems, unpowered or low-powered systems vary damping rate and/or height in response to relatively slow changes in vehicle load. Because of the inflexibility of fixed rate damping and spring element systems, adaptive control systems have been proposed wherein the spring rates, ride heights, and/or damping rates are varied as a result of criteria such as road inputs, vehicle turning, and vehicle loading.
Static height control systems respond to sensed height to actuate height control when the vehicle is not in motion. Relatively slow actuator response time for such systems takes seconds or tens of seconds. An improvement to basic mechanical spring and shock systems includes slow speed leveling and/or height adjustment actuation of a static vehicle via pneumatic springs either manually or automatically controlled. This adjustment requires that the vehicle be moved to a level location while adjusting gas pressure to gas springs (that supplement metal springs) to move the vehicle to a desired height and/or level attitude. Quantities of gas spring components range from one per vehicle for simple rear end up/down actuation to multiple springs per suspension unit for complete height and level attitude actuation.
Dynamic leveling systems respond to numerous inputs to actuate height control and/or damping control when the vehicle is moving. Faster actuation response times for active suspension systems range from under one hundred milliseconds to several hundreds of milliseconds. Recently adopted mechanical shock absorber valve systems respond and adapt to jounce acceleration in approximately 10 milliseconds. A goal of such systems is a damping response time of less than 7 milliseconds, preferably less than 5 ms. Based upon vehicle speed, one type of vehicle height control system automatically lowers the vehicle height at higher vehicle speeds to lower ground effect wind resistance with resultant improved handling and reduced fuel consumption. A separate feature is a process that increases vehicle body height on rough road surfaces.
Existing active suspension system sensing inputs include a mode select switch, stop lamp switch, door switch, alternator, check terminal, diagnosis clear terminal, vertical height, first derivative of height with respect to time (velocity), second derivative of height with respect to time (acceleration), load force using a load cell, gas pressure, hydraulic pressure, ball screw motor torque via torque sensor or current measurement, motor position encoder, motor position resolver, vehicle speed, throttle position, wheel slippage, wheel sensors, body deflection, angular acceleration, lateral acceleration, chassis pitch, chassis roll, brake sensor, and anti-lock braking system inputs.
One representative prior art patent relating to a vehicle active suspension system is U.S. Pat. No. 5,322,321 to Yopp. This patent concerns an active suspension system that includes an electrically powered actuator utilized with a height sensor and a gas spring controlled by a gas supply that pressurizes and vents the gas spring to quickly add or remove a predetermined force as needed in assisting the electrically powered actuator.
The present invention is intended for use with a motor vehicle having at least one fluid-pressurized height adjusting member having first and second separable components. Apparatus constructed in accordance with the invention includes an integrated vehicle ride height system control system. The control system includes an electronic output drive signal circuit and input signal interpretation circuit to electronically interface with at least one position sensor. The position sensor provides output signals related to extent of separation of said first and second separable components of the fluid pressurized height adjusting member.
An exemplary control system also includes electronic input and/or output circuitry to interface with at least one fluid pressure sensor which provides output signals related to a fluid-pressurized height-adjusting member.
The exemplary control system also includes an electronic output circuitry to drive output power control for at least one fluid flow valve which applies pressure to the at least one fluid-pressurized height adjusting member to actuate the height adjusting member to raise the vehicle. The exemplary control system also provides an electronic output coupled to at least one fluid flow valve which releases pressure from the fluid-pressurized height adjusting member to lower the vehicle. The control system also includes electronic output circuitry to control a fluid pressure pump to provide system fluid power.
The Exemplary control system include a programmable controller that implements control algorithms for vehicle height control output functions in response to vehicle input signals.
These and other objects, advantages and features of the invention will become better understood from the following detailed description of a preferred embodiment of the invention which is described in conjunction with the accompanying drawings.